U.S. patent application number 15/035355 was filed with the patent office on 2017-03-16 for method for manufacturing hollow silica particles, hollow silica particles, and composition and thermal insulation sheet comprising same.
This patent application is currently assigned to SUKGYUNG AT CO., LTD .. The applicant listed for this patent is SUKGYUNG AT CO., LTD.. Invention is credited to O Sung KWON, Hyung Sup LIM, Eun Young SONG, Young Cheol YOO.
Application Number | 20170073237 15/035355 |
Document ID | / |
Family ID | 54873834 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170073237 |
Kind Code |
A1 |
LIM; Hyung Sup ; et
al. |
March 16, 2017 |
METHOD FOR MANUFACTURING HOLLOW SILICA PARTICLES, HOLLOW SILICA
PARTICLES, AND COMPOSITION AND THERMAL INSULATION SHEET COMPRISING
SAME
Abstract
Provided are hollow silica particles that have a refractive
index of 1.2-1.4, a thermal conductivity of less than 0.1 W/mK, an
oil absorption rate of 0.1 ml/g or below, a porosity of at least
90% when mixed with a resin, and a particle distribution
coefficient of variation (CV value) of 10% or below. Further
provided are a composition comprising the hollow silica particles,
and a transparent thermal insulation sheet which has a visible
light transmittance of at least 70%, a thermal conductivity of less
than 0.1 W/mK, and a filling rate of particles of 30-80%.
Inventors: |
LIM; Hyung Sup; (Ansan-si,
KR) ; YOO; Young Cheol; (Ansan-si, KR) ; KWON;
O Sung; (Gunpo-si, KR) ; SONG; Eun Young;
(Incheon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUKGYUNG AT CO., LTD. |
Ansan-si |
|
KR |
|
|
Assignee: |
SUKGYUNG AT CO., LTD .
Ansan-si
KR
|
Family ID: |
54873834 |
Appl. No.: |
15/035355 |
Filed: |
April 23, 2015 |
PCT Filed: |
April 23, 2015 |
PCT NO: |
PCT/KR2015/004057 |
371 Date: |
May 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2004/64 20130101;
C08J 2367/02 20130101; C01P 2004/51 20130101; C09D 7/62 20180101;
C01P 2004/62 20130101; C08K 7/26 20130101; C09D 7/69 20180101; C08J
7/0427 20200101; C08K 3/36 20130101; C08K 2201/006 20130101; C09D
7/70 20180101; C09D 179/08 20130101; C01P 2006/60 20130101; C08K
2201/003 20130101; C01P 2004/04 20130101; C01P 2006/19 20130101;
C01P 2004/34 20130101; C01P 2006/32 20130101; C08J 2479/08
20130101; C01B 33/18 20130101 |
International
Class: |
C01B 33/18 20060101
C01B033/18; C08K 7/26 20060101 C08K007/26; E06B 9/24 20060101
E06B009/24; C08J 7/04 20060101 C08J007/04; C09D 179/08 20060101
C09D179/08; E06B 3/00 20060101 E06B003/00; C09D 7/12 20060101
C09D007/12; C08K 3/36 20060101 C08K003/36 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2014 |
KR |
10-2014-0065775 |
Apr 21, 2015 |
KR |
10-2015-0055981 |
Claims
1. A hollow silica particle having a refractive index of 1.2 to
1.4, a thermal conductivity of less than 0.1 W/mK, an oil
absorption rate of 0.1 ml/g or less, a porosity of 90% or more when
mixed with a resin, and a particle size distribution coefficient of
variation (CV value) of 10% or less.
2. The hollow silica particle of claim 1, wherein an average
diameter of the particle is 1 .mu.m or less, and an inner diameter
of a hollow portion is 10% to 90% of the average diameter of the
particle.
3. The hollow silica particle of claim 1, wherein the particle has
a sphericity of 0.9 or more.
4. The hollow silica particle of claim 1, wherein a surface of the
particle has an --OH group and a phenyl group as a functional
group.
5. The hollow silica particle of claim 1, wherein a thickness of a
shell is 5% to 45% of the average particle diameter.
6. A method of manufacturing hollow silica particles, the method
comprising steps of: (a) adding 0.1 mol % to 2 mol % of silane to
an aqueous solution and stirring to generate silane droplets; (b)
adding an acid to the aqueous solution to hydrate the silane
droplets; (c) forming primary particles through bonding between the
silane droplets by adding a basic aqueous solution to a reaction
solution of step (b); (d) forming a shell through polymerization of
the primary particles by stirring the reaction solution to which
the basic aqueous solution is added; (e) etching inside of the
shell with an organic solvent to form a hollow; and (f) filtering
and drying the solution.
7. The method of claim 6, wherein the primary particles have a
polyphenylsilsesquioxane (PPSQ) structure.
8. The method of claim 6, wherein the reaction solution has a pH of
1 to 5 after the adding of the acid in step (b).
9. The method of claim 6, wherein stirring time in step (b) is in a
range of 0.5 minutes to 10 minutes.
10. The method of claim 6, wherein the reaction solution has a pH
of 10 or more after the adding of the basic solution in step
(c).
11. The method of claim 6, wherein a thickness of the insoluble
shell is 5% to 45% of an average particle diameter.
12. The method of claim 6, wherein the silane comprises at least
one selected from the group consisting of phenyl-based silane,
tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS),
SiCl.sub.4, and silane having an organic group other than a phenyl
group, or a mixture thereof.
13. The method of claim 12, wherein the phenyl-based silane is
phenyltrimethoxysilane (PTMS).
14. The method of claim 12, wherein the mixture of the silanes
comprises 80 wt % or more of the phenyl-based silane and 20 wt % or
less of the other silane.
15. The method of claim 6, wherein the basic solution comprises
NH.sub.4OH, or an alkylamine solution selected from the group
consisting of tetramethyl ammonium hydroxide (TMAH), octylamine
(OA, CH.sub.3(CH.sub.2).sub.6CH.sub.2H.sub.2), dodecylamine (DDA,
CH.sub.3(CH.sub.2).sub.10CH.sub.2NH.sub.2), hexadecylamine (HDA,
CH.sub.3(CH.sub.2).sub.14CH.sub.2NH.sub.2), 2-aminopropanol,
2-(methylphenylamino)ethanol, 2-(ethylphenylamino)ethanol,
2-amino-1-butanol, (diisopropylamino)ethanol,
2-diethylaminoethanol, 4-aminophenylaminoisopropanol,
N-ethylaminoethanol, monoethanolamine, diethanolamine,
triethanolamine, monoisopropanolamine, diisopropanolamine,
triisopropanolamine, methyldiethanolamine,
dimethylmonoethanolamine, ethyldiethanolamine, and
diethylmonoethanolamine.
16. The method of claim 6, wherein reaction temperatures in step
(b) and step (d) are in a range of 40.degree. C. to 80.degree.
C.
17. The method of claim 6, further comprising a step of (g)
performing sonication on a filtrate after the filtering in step
(f).
18. The method of claim 6, wherein drying temperature is
250.degree. C. or less.
19. The method of claim 6, further comprising a step of (i)
modifying surfaces of the hollow silica particles after step
(f).
20. A composition comprising the hollow silica particles of claim
1, a resin, and a solvent.
21. The composition of claim 20, wherein the hollow silica
particles are included in an amount of 30 wt % to 80 wt % based on
the total composition.
22. The composition of claim 20, wherein the resin is included in
an amount of 20 wt % to 70 wt % based on the total composition.
23. The composition of claim 20, wherein the resin has a refractive
index of less than 1.5.
24. The composition of claim 20, wherein the resin comprises at
least one selected from the group consisting of an acrylate-based
polymer resin, a polyimide (PI) resin, a C-polyvinyl chloride (PVC)
resin, a polyvinylidene fluoride (PVDF) resin, an acrylonitrile
butadiene styrene (ABS) resin, and chlorotrifluoroethylene (CTFE),
or a mixture thereof.
25. The composition of claim 20, further comprising at least one
selected from the group consisting of a hard coating agent, an
ultraviolet (UV) blocking agent, or an infrared (IR) blocking
agent.
26. A thermal insulation sheet having a visible light transmittance
of 70% or more, a thermal conductivity of less than 0.1 W/mK, and a
filling rate of hollow silica particles of 30% to 80%, the thermal
insulation sheet comprising: a base material; and a coating layer
formed by coating the base material with the composition of claim
21.
27. The thermal insulation sheet of claim 26, wherein the coating
layer has a UV and IR blocking function.
28. The thermal insulation sheet of claim 26, wherein the base
material comprises a sheet of a polymer material, a textile, a
film, or glass.
29. A method of manufacturing a thermal insulation sheet, the
method comprising: preparing a base material; forming a coating
layer by coating the base material with the composition of claim
20; and curing the coating layer.
Description
TECHNICAL FIELD
[0001] The present invention disclosed herein relates to hollow
silica particles having complex properties and a method of
manufacturing the same, and a composition and a thermal insulation
sheet which include the hollow silica particles.
BACKGROUND ART
[0002] The cost of heating and cooling buildings is approximately
25 trillion won or more annually. Recently, the use of glass as an
exterior decoration material is being increased and, among heating
and cooling energy, the rate of heat loss through windows accounts
for the largest share with 39% of total heat loss. Thus, measures
to reduce the increasing heating and cooling energy consumption are
urgent and, in addition, there emerges a need to improve window
insulation performance. In recent years, there is a need to develop
a thermal insulation material for manufacturing a heat insulation
sheet, which satisfies two characteristics of transparency and
thermal insulation, and to develop an eco-friendly new material.
Hollow silica particles may be used as one of such thermal
insulation materials, wherein KR 101180040 discloses a method of
manufacturing a hollow composite having an average particle
diameter of 20 nm to 500 nm, as the hollow composite in which
silica is doped with magnesium fluoride, but the method is related
to a method of manufacturing hollow particles by preparing core and
shell of silica particles through a sol-gel method and then
removing the core. KR 101359848 only discloses a method of
manufacturing hollow silica, which includes the steps of
synthesizing silver nanocrystals by using a polyol solvent,
synthesizing silver-silica core-shell nanoparticles by coating the
silver nanocrystals with silica, and etching the silver core of the
silver-silica core-shell nanoparticles, and hollow silica prepared
accordingly. Therefore, it may be difficult to simply and stably
manufacture hollow silica particles having physical properties,
such as a high visible light transmittance, a high refractive
index, a low thermal conductivity, a degree of monodispersion, a
low oil absorption rate, and a high porosity, by hollow silica
manufacturing techniques known to date. In addition, there is a
limitation in that physical properties of conventional hollow
silica are not sufficient to manufacture a thermal insulation sheet
having excellent thermal insulation performance as well as
transparency.
DISCLOSURE OF THE INVENTION
Technical Problem
[0003] The present invention provides hollow silica particles
having a combination of advantageous physical properties, for
example, low thermal conductivity as well as low refractive index.
The present invention also provides a composition and a transparent
thermal insulation sheet which include the hollow silica
particles.
Technical Solution
[0004] In accordance with an embodiment of the present invention, a
hollow silica particle has complex physical properties in which a
refractive index is 1.2 to 1.4, a thermal conductivity is less than
0.1 W/mK, an oil absorption rate is 0.1 ml/g or less, a porosity is
90% or more when mixed with a resin, and a particle size
distribution coefficient of variation (CV value) is 10% or
less.
[0005] An average diameter of the particle may be 1 .mu.m or less,
an inner diameter of a hollow portion may be 10% to 90% of the
average diameter of the particle, and a thickness of a shell may be
5% to 45% of the average particle diameter. For example, the hollow
silica particle may have an average diameter of 500 nm or less and
an inner diameter of the hollow portion of 40 nm or more. In order
to maximize a filling rate of particles when manufacturing a
thermal insulation sheet, the average diameter of the particle may
be 500 nm or less and the inner diameter of the hollow portion may
be 40 nm or more.
[0006] Also, the hollow silica particle may be formed from a
phenyl-based silane, and an --OH group and a phenyl group are
present as a functional group on a surface of the particle so that
strength of the particle may be high.
[0007] Furthermore, with respect to the particle manufactured by a
method of the present invention, since fine pores are hardly
present on the surface of the particle, the oil absorption rate is
0.1 ml/g or less and the porosity is 90% or more when mixed with a
resin. Thus, the collapse of particle shape and hollow does not
occur when charged into a binder such as a resin. Accordingly,
since particle properties, such as sphericity, average particle
diameter, refractive index, and thermal conductivity, are not
changed and stably maintained, the particle has properties suitable
for being highly charged into the binder such as the resin.
[0008] The hollow particle of the present invention has a
sphericity of 0.9 or more, wherein at least 90% of the silica
particle is in the form of a sphere having a uniform convex grain
contour in which a flat surface, corner, or recognizable recessed
portion is not present.
[0009] In accordance with another embodiment of the present
invention, a method of manufacturing hollow silica particles
includes the following steps of:
[0010] (a) adding 0.1 mol % to 2 mol % of silane to an aqueous
solution and stirring to generate silane droplets;
[0011] (b) adding an acid to the aqueous solution to hydrate the
silane droplets;
[0012] (c) forming primary particles through bonding between the
silane droplets by adding a basic aqueous solution to a reaction
solution of step (b);
[0013] (d) forming a shell through polymerization of the primary
particles by stirring the reaction solution to which the basic
aqueous solution is added;
[0014] (e) etching inside of the shell with an organic solvent to
form a hollow; and
[0015] (f) filtering and drying the solution.
[0016] In the above manufacturing method, the finally manufactured
particles have an average diameter of 1 .mu.m or less, and an inner
diameter of a hollow portion is 10% to 90% of the average diameter
of the particles.
[0017] The reaction solution has a pH of 1 to 5 after the adding of
the acid in step (b), and hydration time in step (b) is in a range
of 1 minute to 10 minutes.
[0018] The basic aqueous solution in step (c) has a pH of 10 or
more, and the polymerization is performed to allow a thickness of
the insoluble shell to be 5% to 45% of the average particle
diameter.
[0019] The silane includes at least one selected from the group
consisting of phenyl-based silane, tetraethyl orthosilicate (TEOS),
tetramethyl orthosilicate (TMOS), SiCl.sub.4, and silane having an
organic group other than a phenyl group, or a mixture thereof. In a
case in which a mixture of the phenyl-based silane and the other
silane is used, 80 wt % or more of the phenyl-based silane and 20
wt % or less of the other silane may be mixed and used, and
phenyltrimethoxysilane (PTMS) may be used as the phenyl-based
silane.
[0020] The basic solution in step (d) includes NH.sub.4OH or an
inorganic base, such as alkylamines, and the alkylamine is selected
from the group consisting of tetramethyl ammonium hydroxide (TMAH),
octylamine (OA, CH.sub.3(CH.sub.2).sub.6CH.sub.2H.sub.2),
dodecylamine (DDA, CH.sub.3(CH.sub.2).sub.10CH.sub.2NH.sub.2),
hexadecylamine (HDA, CH.sub.3(CH.sub.2).sub.14CH.sub.2NH.sub.2),
2-aminopropanol, 2-(methylphenylamino)ethanol,
2-(ethylphenylamino)ethanol, 2-amino-1-butanol,
(diisopropylamino)ethanol, 2-diethylaminoethanol,
4-aminophenylaminoisopropanol, N-ethylaminoethanol,
monoethanolamine, diethanolamine, triethanolamine,
monoisopropanolamine, diisopropanolamine, triisopropanolamine,
methyldiethanolamine, dimethylmonoethanolamine,
ethyldiethanolamine, and diethylmonoethanolamine.
[0021] Reaction temperatures in step (b) and step (d) may be in a
range of 40.degree. C. to 80.degree. C., and the method may prepare
a smoother surface by further including a step of (g) performing
sonication on a filtrate after the filtering in step (f).
[0022] The drying after the filtering may be performed at a
temperature of 250.degree. C. or less, for example, 150.degree. C.
or less.
[0023] The method may further include a step of (i) modifying
surfaces of the hollow silica particles after step (0, and the use
of the particles may be expanded by providing a functional group on
the surface of the particles.
[0024] In accordance with another embodiment of the present
invention, a composition includes the hollow silica particles of
the present invention, a resin, and a solvent. The hollow silica
particles may be included in an amount of 30 wt % to 80 wt % and
the resin may be included in an amount of 20 wt % to 70 wt % based
on the total composition.
[0025] The resin in the composition may have a refractive index of
less than 1.5, and at least one selected from the group consisting
of an acrylate-based polymer resin, a polyimide (PI) resin, a
C-polyvinyl chloride (PVC) resin, a polyvinylidene fluoride (PVDF)
resin, an acrylonitrile butadiene styrene (ABS) resin, and
chlorotrifluoroethylene (CTFE), or a mixture thereof may be
used.
[0026] Also, the composition may further include at least one
selected from the group consisting of a hard coating agent, an
ultraviolet (UV) blocking agent, or an infrared (IR) blocking agent
to provide additional functionality.
[0027] In accordance with another embodiment of the present
invention, a thermal insulation sheet having a visible light
transmittance of 70% or more, a thermal conductivity of less than
0.1 W/mK, and a filling rate of hollow silica particles of 30% to
80% is manufactured by preparing a base material, forming a coating
layer by coating the base material with the composition, and curing
the coating layer. The coating layer may further have a UV and IR
blocking function. A sheet of a polymer material, a textile, a
film, or glass may be used as the base material of the thermal
insulation sheet.
Advantageous Effects
[0028] According to the present invention, hollow silica particles
having properties, such as a refractive index of 1.2 to 1.4, a
thermal conductivity of less than 0.1 W/mK, an oil absorption rate
of 0.1 ml/g or less, a porosity of 90% or more when mixed with a
resin, and a particle size distribution coefficient of variation
(CV value) of 10% or less, may be provided by a simple and stable
manufacturing method.
[0029] Also, a composition, which includes the hollow silica
particles having the above physical properties, may be provided,
and accordingly, a thermal insulation sheet having excellent
thermal insulation performance as well as transparency may be
provided in which a visible light transmittance is 70% or more, a
thermal conductivity is less than 0.1 W/mK, and a particle filling
rate is 30% to 80%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is schematic views illustrating a hydrated
phenyltrimethoxysilane (PTMS) droplet, a primary particle, and a
structure of a particle having a shell formed thereon in a
manufacturing process of the present invention;
[0031] FIG. 2 is transmission electron microscope (TEM) images of
hollow silica particles having an average particle diameter of 100
nm according to an example of the present invention;
[0032] FIG. 3 is TEM images of particles which are formed during a
reaction at a temperature of 85.degree. C. according to a
comparative example;
[0033] FIG. 4 is TEM images obtained by hydrolyzing the silica
particles according to the example of the present invention at
60.degree. C. for 30 seconds and then etching the silica
particles;
[0034] FIG. 5 is TEM images of particles after the sonication of
the particles of FIG. 4; and
[0035] FIG. 6 is TEM images of particles of the present invention
which are obtained after polyphenylsilsesquioxane (PPSQ) is
polymerized, cleaned, dispersed in methanol, and then etched.
MODE FOR CARRYING OUT THE INVENTION
[0036] A manufacturing process and physical properties of hollow
silica particles of the present invention will be described in
detail.
[0037] Manufacture of Hollow Silica Particles
[0038] With respect to hollow silica particles of the present
invention, silane is used as a starting raw material, is stirred in
an aqueous solution to generate droplets, and is then hydrated by
adding an acid. Then, primary particles are formed through bonding
between the droplets by adding a basic aqueous solution and are
then polymerized to form a shell. Then, the inside of the shell is
etched with an organic solvent to form a hollow and final hollow
silica particle powder is manufactured through filtration and
drying. In this case, a step of performing sonication on the
filtrate may be further included.
[0039] 1. Raw Material
[0040] At least one selected from the group consisting of
phenyl-based silane, tetraethyl orthosilicate (TEOS), tetramethyl
orthosilicate (TMOS), SiCl.sub.4, and silane having an organic
group other than a phenyl group, or a mixture thereof may be used
as a raw material of hollow silica particles. In a case in which a
mixture of the phenyl-based silane and the other silane is used, 80
wt % or more of the phenyl-based silane and 20 wt % or less of the
other silane may be mixed and used, and particularly,
phenyltrimethoxysilane (PTMS, C.sub.9H.sub.14O.sub.3Si) having a
structure of the following Formula 1 may be used as the
phenyl-based silane.
[0041] In a case in which the PTMS and at least one silane selected
from TEOS, TMOS, SiCl.sub.4, and silane having an organic group
other than a phenyl group are mixed and used, the PTMS and the at
least one silane may be mixed in a weight ratio of 4:1.
[0042] As a concentration of the silane, when the silane is used in
an amount of 0.1 mol % or less in the aqueous solution, small
particles having a diameter of about 1 .mu.m or less may be
obtained.
##STR00001##
[0043] 2. Droplet Generation
[0044] When 0.1 mol % to 2 mol % of the silane is added to the
aqueous solution, the silane is not mixed with the aqueous
solution, and thus, separation occurs. When the aqueous solution is
continuously stirred, silane droplets are formed and dispersed in
the aqueous solution.
[0045] 3. Droplet Hydration
[0046] When an acid is added to the aqueous solution, --OR groups
of the silane are substituted with --OH groups by the catalytic
role of the acid as illustrated in (a) of FIG. 1, and when the
aqueous solution is continuously stirred, hydrated silane droplets
are uniformly mixed with the aqueous solution. HCl, HNO.sub.3, or
H.sub.2SO.sub.4 may be used as the acid, and a reaction solution
may have a pH of 0.5 to 5. In this case, since chains of the silane
are cut off as the pH of the reaction solution is low, the diameter
of the particle is decreased. Thus, when the reaction solution is
highly acidic at a pH of 1, a small amount of the silane must be
used. The reason for this is that since the reaction easily
proceeds in the form of a gel or a hollow is not formed in the
particle when the amount of the silane is large, it is difficult to
control the particle generation. Also, if the pH is 5 or more,
particle and hollow may not be formed when a small amount of the
silane is used.
[0047] The diameter of the finally formed particle becomes smaller
as the stirring time increases after the addition of the acid, but
the particles are agglomerated to be a gel so that the hollow is
difficult to be formed. When the stirring time is excessively
short, the hydration of the silane droplets insufficiently occurs,
and thus, it is difficult to form hollow particles. Thus, the
stirring time may be between 0.5 minutes to 10 minutes, for
example, 1 minute to 5 minutes.
[0048] There is no difference between diameters of the droplet when
a size of a stirrer to that of a reactor is about 80% and stirring
speed is greater than 200 rpm, but, since the particle diameter
increases when the stirring speed is 200 rpm or less, the stirring
speed may be 200 rpm or more. The diameter of the hydrated droplet
may be in a range of 8 .mu.m to 12 .mu.m, and the final particle
diameter is determined depending on the diameter of the
droplet.
[0049] A temperature of the reaction may be in a range of
40.degree. C. to 80.degree. C. The particle generation may be
difficult at a temperature of less than 40.degree. C., and, at a
high concentration, the particles may be agglomerated to be easily
in the form of a gel and a thickness of the shell may be increased
to reduce a diameter of the hollow. In a case in which the
temperature is greater than 80.degree. C., it is difficult to
control reaction conditions due to the evaporation of the base, and
hollow particles are not formed because the inside of the shell is
not melted. A hydration equation of PTMS is as follows.
[Reaction Equation 1]
PhSi(OMt).sub.3+H.sub.2O->PhSi(OH)(OMt).sub.2
PhSi(OH)(OMt).sub.2+H.sub.2O->PhSi(OH).sub.2(OMt)
PhSi(OH).sub.2(OMt)+H.sub.2O->PhSi(OH).sub.3
[0050] 4. Primary Particle Formation
[0051] When a basic solution is added to the solution in which the
silane is hydrated, the basic solution acts as a catalyst to form
primary particles due to a reaction between the silane droplets as
illustrated in (b) of FIG. 1. A base, such as NaOH, Ca(OH).sub.2,
KOH, and NH.sub.4OH, for example, NH.sub.4OH or an inorganic base,
such as alkylamines, is used as the basic solution, and the total
reaction solution is allowed to have a pH of 10 or more. The
alkylamine is selected from the group consisting of tetramethyl
ammonium hydroxide (TMAH), octylamine (OA,
CH.sub.3(CH.sub.2).sub.6CH.sub.2H.sub.2), dodecylamine (DDA,
CH.sub.3(CH.sub.2).sub.10CH.sub.2NH.sub.2), hexadecylamine (HDA,
CH.sub.3(CH.sub.2).sub.14CH.sub.2NH.sub.2), 2-aminopropanol,
2-(methylphenylamino)ethanol, 2-(ethylphenylamino)ethanol,
2-amino-1-butanol, (diisopropylamino)ethanol,
2-diethylaminoethanol, 4-aminophenylaminoisopropanol, N-ethylamino
ethanol, monoethanolamine, diethanolamine, triethanolamine,
monoisopropanolamine, diisopropanolamine, triisopropanolamine,
methyldiethanolamine, dimethylmonoethanolamine,
ethyldiethanolamine, and diethylmonoethanolamine.
[0052] When the reaction temperature is less than 40.degree. C.,
since the particles are agglomerated to be easily in the form of a
gel, the generation of the hollow particles may be difficult and
the thickness of the shell may be increased to reduce the diameter
of the hollow. When the temperature is greater than 80.degree. C.,
it is difficult to control reaction conditions due to the
evaporation of the base, and hollow particles are not formed
because the inside of the shell is not melted. Thus, the reaction
may be performed in a temperature range of 40.degree. C. to
80.degree. C.
2Ph-Si(OH).sub.3.fwdarw.Ph-Si(OH).sub.2--O--Si(OH).sub.2-Ph
[Reaction Equation 2]
[0053] 5. Shell Formation
[0054] The aqueous solution, to which the basic solution is added,
is stirred to polymerize the primary particles through siloxane
bonds and thus, a shell, which is insoluble in an organic solvent,
is formed. The thickness of the shell may be 5% to 45% of an
average diameter of the silica particle. In a case in which PTMS is
used as a raw material to form particles, the shell may have a
networked polyphenylsilsesquioxane (PPSQ) structure.
Ph-Si(OH).sub.2--O--Si(OH).sub.2-Ph.fwdarw.+n[Ph-Si(OH).sub.3].fwdarw.ne-
tworked polyphenylsilsesquioxane (PPSQ) [Reaction Equation 3]
##STR00002##
[0055] 6. Etching
[0056] A silane oligomer and an unreacted droplet are present in
the inside of the insoluble shell, and the silane oligomer and
unreacted droplet are etched using an organic solvent to form a
hollow in the inside of the shell.
[0057] Any organic solvent generally used, including ethanol or
methanol, may be used as the organic solvent.
[0058] Sonication is further performed on the filtrate using a
sonicator to remove impurities on the surfaces of the particles,
and thus, the surfaces of the particles may be made smoother. The
sonication may be performed for 5 seconds to 40 minutes.
[0059] 7. Filtration and Drying
[0060] When the filtrate is dried at a temperature of less than
250.degree. C., for example, 150.degree. C., in a vacuum oven for 1
hour to 10 hours, evaporation or sublimation of moisture occurs at
a temperature corresponding to vacuum, and thus, the filtrate is
dried.
[0061] A step of modifying the surface of the particles by a known
method, such as nitrification, sulfonation, amination, and
halogenation, through the treatment of the formed hollow silica
particles with a silane coupling agent may be further included. A
silane-based, aluminum-based, titanium-based, or zirconium-based
coupling agent may be used as the silane coupling agent. The hollow
silica particles thus surface modified may be used in various areas
such as functional ceramics, microcapsules, nanoreactors, drug
delivery systems (DDS), catalysts, and sensors. When the surface is
treated with the surface treatment agent as described above,
dispersibility in a hydrophobic dispersion medium, such as a resin
or an organic solvent, is improved, and adhesion to the resin or
peel strength may also be improved.
[0062] Also, since a template is not required during the
manufacture of the hollow particles and a sintering process
requiring a lot of time and high energy costs is not necessary,
hollow silica particles may be obtained by a simple manufacturing
process.
[0063] Hollow Silica Particles
[0064] The hollow silica particles manufactured by the above
manufacturing method have monodisperse physical properties, such as
a refractive index of 1.2 to 1.4, a thermal conductivity of less
than 0.1 W/mK, an oil absorption rate of 0.1 ml/g or less, a
porosity of 90% or more when mixed with a resin, and a particle
size distribution coefficient of variation (CV value) of 10% or
less. Also, the hollow silica particles are true spherical
particles in which an average diameter of the particles is 1 .mu.m
or less, an inner diameter of a hollow portion is 10% to 90% of the
average diameter of the particles, the thickness of the shell is 5%
to 45% of the average particle diameter, and a sphericity is 0.9 or
more.
[0065] Hereinafter, physical properties of the hollow silica
particles of the present invention and measurement methods thereof
will be described.
[0066] 1) Refractive Index
[0067] First, hollow silica is dispersed in a sorbitol syrup (70%
sorbitol)/water mixture. Degassing is generally performed for 1
hour, light transparency of the dispersed solution is then measured
at 589 nm by using a spectrophotometer, and water is used as a
blind sample. A refractive index of each dispersed solution is
measured using an Abbe refractometer. A range of the refractive
index, in which the light transmittance is greater than 70%, may be
obtained from a graph of the light transmittance versus the
refractive index. The maximum light transmittance of the sample and
a refractive index, from which the maximum light transmittance is
obtained, may also be obtained from the graph.
[0068] 2) Thermal Conductivity
[0069] For the measurement of thermal conductivity, the center of a
thermal insulation sheet having a length of 30 cm, a width of 30
cm, and a thickness of 5 cm is cut into the shape of a square with
a length of 24 cm and a width of 24 cm to form a frame. An aluminum
foil having a length of 30 cm and a width of 30 cm is adhered to
one side of the frame to form a recessed portion and it is used as
a sample stand. Also, a surface covered with the aluminum foil is
determined as a bottom surface of the sample stand and another
surface in a thickness direction of the thermal insulation sheet is
determined as a top surface. Thermal insulation material powder is
charged into the recessed portion without tapping or pressurization
to perform leveling, and an aluminum foil having a length of 30 cm
and a width of 30 cm disposed on the top surface is used as a
measurement sample. Thermal conductivity of the measurement sample
at 30.degree. C. is measured using a heat flow meter, HFM 436
Lambda (brand name, manufactured by NETZSCH Group). According to
JIS A 1412-2, calibration is performed in advance using a NIST SRM
1450c standard plate for calibration having a density of 163.12
kg/m.sup.3 and a thickness of 25.32 mm at 15.degree. C., 20.degree.
C., 24.degree. C., 30.degree. C., 40.degree. C., 50.degree. C.,
60.degree. C., and 65.degree. C. under a condition in which a
temperature difference between a high-temperature side and a
low-temperature side is 20.degree. C. Thermal conductivity at
800.degree. C. is measured according to the method of JIS A 1421-1.
Two disc-shaped thermal insulation sheets having a diameter of 30
cm and a thickness of 20 mm are used as measurement samples, and a
guarded hot plate method thermal conductivity instrument
(manufactured by Eiko Seiki Co., Ltd.) is used as a measuring
instrument.
[0070] 3) Oil Absorption Rate
[0071] The hollow silica particles of the present invention have
characteristics in that their spherical surfaces are substantially
smooth even if separate sintering and surface treatment are not
performed after the manufacture of the particles. Herein, the term
"smooth" denotes that fine pores are hardly present on the surfaces
and there are no random uneven portions, such as depressions, gaps,
flaws, cracks, protrusions, and grooves, on the surface of the
shell. These surface characteristics are absent for hollow silica
particles obtained by a conventional manufacturing method.
Smoothness of the particles of the present invention may be
measured by a scanning electron microscope and may be confirmed by
the oil absorption rate and the porosity when mixed with a
resin.
[0072] The oil absorption rate was measured by using a rub-out
method (ASTM D281). The method is based on a principle in which
linseed oil is mixed with silica by rubbing a linseed oil/silica
mixture on a smooth surface using a spatula until a stiff putty
paste is formed. An oil absorption rate of silica may be calculated
by measuring the amount of the oil which is required to obtain a
paste mixture curled when sprayed, wherein this represents a volume
of the oil which is required for unit weight of the silica in order
to saturate silica adsorption capacity. A high oil absorption level
denotes that the plurality of fine pores is present on the surface
or the diameter of the fine pores is large, and a low oil
absorption level denotes that fine pores are hardly present on the
surface of the shell of the silica particles. The oil absorption
rate may be determined by the following equation.
Oil absorption rate=amount of oil ml/silica 100 g
[0073] 4) Porosity
[0074] Porosity may be identified by an amount of a resin soaked
into a hollow when the hollow silica particles are mixed with the
resin. The amount of the resin soaked into the hollow is measured
in the same manner as the oil absorption rate and a small amount of
the resin indicates that the hollow is maintained.
[0075] That is, a structure, in which the surface of particles is
smooth and fine pores are hardly present, denotes that, in a case
in which the hollow silica particles are charged into a resin,
since the resin constituting a binder or oil is not soaked into the
hollow of the particles, the porosity is increased to obtain
transparency and low thermal conductivity of the particles, and an
increase in transparent thermal insulation performance of the
thermal insulation sheet coated with a composition including the
above particles is possible.
[0076] 5) Particle Size Distribution Coefficient of Variation (CV
Value) (Degree of Monodispersion)
[0077] Particles were imaged using a scanning electron microscope
(.times.250,000) and an average particle diameter of 25 particles
of the image was measured using an image analysis system to
calculate a coefficient of variation (CV value) for particle
diameter distribution. Specifically, for 250 particles, a diameter
of each particle was measured and an average particle diameter and
a standard deviation of the particle diameter were obtained from
the measured diameter values to calculate the coefficient of
variation from the following equation.
Particle size distribution coefficient of variation (CVD
(%))=(standard deviation of particle diameter (.sigma.)/average
particle diameter (Dn)).times.100
[0078] 6) Sphericity
[0079] Characteristics of the silica particles of the present
invention having a very round shape are analyzed by measuring
scanning electron microscope (SEM) images illustrating a
cross-sectional structure of the particle and are represented by a
ratio (DS/DL) of a short diameter (DS) to a long diameter (DL). A
representative sample of the silica particles was collected and
tested by an SEM. As illustrated in the electron microscope image
of FIG. 2, a sphericity (S.sub.80) of the particles of the present
invention is 0.9 or more, and thus, it may be understood that the
particles of the present invention are spherical particles close to
a true sphere. The expression "S.sub.80" used in the present
application is defined and calculated as follows. An SEM image
magnified 20,000 times, as a representative example of the silica
particle sample, is loaded into a photo imaging software and a
contour (two-dimensional) of each particle is traced. Particles,
which are in close proximity to each other but are not attached to
each other, must be considered as separate particles for
evaluation. The particles subjected to contour analysis are
subsequently filled with a color, and the image is loaded into a
particle characterization software (for example, MAGE-PRO PLUS
available from Media Cybernetics, Inc. (Bethesda, Md.)) that may
determine a circumference and an area of the particle. The
sphericity of the particle may be subsequently calculated by the
following equation.
Sphericity=circumference.sup.2/4.pi..times.area
[0080] In the above equation, the circumference is a software
measured circumference which is derived from the contour analyzed
trace of the particle, and the area is a software measured area
within the traced circumference of the particle. The above
calculation is performed on each particle that is entirely
appropriate in the SEM image. These values are subsequently
classified according to a value, and the bottom 20% of these values
are discarded. The remaining 80% of these values are averaged to
obtain the S.sub.80. It was confirmed that the sphericity
(S.sub.80) of the particles of FIG. 2 was 0.98.
[0081] 7) Average Particle Diameter and Thickness of Shell
[0082] "Average diameter" is understood as a diameter which is
averaged for all particles in the sample.
[0083] A representative sample of the silica particles was
collected and a diameter of the silica particles was measured by an
SEM. An inner diameter of the hollow portion was measured by a
transmission electron microscope (TEM).
[0084] An average diameter of the hollow particles of the present
invention is generally 1 .mu.m or less, particularly, 500 nm or
less, and more particularly, 100 nm or less. In a case in which the
average diameter is greater than 1 .mu.m, since the hollow
particles may not be completely filled within the thickness of the
coating layer during the manufacture of the thermal insulation
sheet, a filling rate may be reduced. Thus, a targeted thermal
insulation effect may not be achieved.
[0085] The hollow silica particles of the present invention are
particles in which the average diameter is 1 .mu.m or less, and the
inner diameter of the hollow portion is 10% to 90% of the average
diameter of the particles. With respect to particles having an
average diameter of 100 nm, the thermal insulation effect was good
when the inner diameter of the hollow portion was 40 nm or more.
Since the hollow silica particles are stable during the reaction
when the thickness of the shell is 5% to 45% of the average
particle diameter, the hollow silica particles may be used as a
thermal insulation material.
[0086] 8) Functional Group
[0087] Also, in a case in which phenyl-based silane is used as a
raw material, the particles have an --OH group and a phenyl group
as a functional group on the surfaces thereof, and, since a
refractive index may be increased due to the phenyl group in
comparison to other silica particles, the particles may have a
refractive index similar to that of a resin. Thus, a transparent
thermal insulation sheet may be manufactured because a difference
in the refractive indices between the particles and the resin may
be minimized.
[0088] Coating Composition Including Hollow Silica Particles and
Resin
[0089] According to another embodiment of the present invention, a
composition for forming a transparent thermal insulation coating
layer on a base material is provided. The composition of the
present invention may be prepared by mixing the hollow silica
particles having complex physical properties as described above, a
resin, and an organic solvent.
[0090] The hollow silica particles may be included in an amount of
30 wt % to 80 wt % in a total composition of the present invention.
In a case in which the amount is less than 30 wt %, thermal
insulation performance of the coating layer may not be achieved,
and, in a case in which the amount is greater than 80 wt %, the
transparency may decrease and the amount of the resin may be
reduced to reduce a curing efficiency.
[0091] The resin may be included in an amount of 20 wt % to 70 wt %
in the total composition of the present invention. In order to
prepare a transparent liquid by controlling a refractive index with
respect to the silica particles, the refractive index of the resin
may be less than 1.5, and a resin having a refractive index similar
to that of the hollow particles may be selected among ultraviolet
(UV)-curable resins and used.
[0092] Examples of the UV-curable resin may be a urethane resin, an
acryl resin, a polyester resin, an epoxy resin, and a mixture
thereof, but the present invention is not limited thereto. At least
one of an acrylate-based polymer resin, a polyimide (PI) resin, a
C-polyvinyl chloride (PVC) resin, a polyvinylidene fluoride (PVDF)
resin (heat resistance temperature of about 300.degree. C.), an
acrylonitrile butadiene styrene (ABS) resin, and
chlorotrifluoroethylene (CTFE), or a mixture thereof may be used as
a resin having low thermal conductivity.
[0093] The composition may further include a hard coating agent, a
UV blocking agent, or an infrared (IR) blocking agent, and a known
additive may be used as the above additive, but an additive
providing additional functions may be further included if
necessary.
[0094] The "composition" used in the present application denotes
any liquid, liquefiable, or mastic composition including silica
which is converted into a solid film after the application to the
base material. The composition may be applied to an inner or outer
surface of any structure.
[0095] The composition includes a hollow silica particle product
and the silica product described in the present application has
specific physical properties including hardness, sphericity,
refractive index, oil absorption rate, and thermal conductivity
which are useful to provide thermal insulation and transparency of
the composition. The composition may be any coating composition and
may be applied to any base material. Since the composition exhibits
excellent transparency and thermal insulation while maintaining
integrity of a polymer and pigment matrix that may exist in the
coating, the composition is suitable for a coating on thermal
insulation sheets, windows in housing and construction sectors, and
car windows. Also, since the composition described in the present
application not only exhibits excellent thermal insulation and
transparent characteristics but also improves physical properties
of a formulation, the composition is suitable for a plastic
compound and a masterbatch formulation.
[0096] Thermal Insulation Sheet
[0097] According to another embodiment of the present invention, a
thermal insulation sheet may be manufactured by preparing a base
material and forming a coating layer by laminating or coating and
UV curing the composition of the present invention on the base
material. Any appropriate coating method known in the art may be
used as the coating method, and examples of the known method may be
gravure coating, offset gravure coating, two and three roll
pressure coating, two and three roll reverse coating, one and two
roll kiss coating, trailing blade coating, nip coating,
flexographic coating, inverted knife coating, polishing bar
coating, and wire wound doctor coating. After the coating, the
coating layer is cured by UV light and the curing treatment is
usually completed in a relatively short period time of about 1
second to about 60 seconds.
[0098] The base material, on which the coating layer is formed by
using the composition, is not particularly limited, but, for
example, may include inorganic base materials represented by glass,
metal base materials, and organic base materials represented by
polycarbonate or polyethylene terephthalate, an acryl resin, a
fluorine resin, triacetyl cellulose, and a polyimide resin. For
example, the base material may include a sheet of a polymer
material, a textile, a film, or glass, and particularly, a film
base material may include a generally applicable film such as
polyethylene terephthalate (PET) and polyethylene (PE). The same
base material may be used alone, and a base material, in which
different materials are laminated, may be used. Also, at least one
layer of different layers may be formed in advance on the surface
of the base material. Examples of the different layer may be an
ultraviolet curable hard coat layer, an electron beam curable hard
coat layer, and a thermosetting hard coat layer.
[0099] A thickness of the coating layer may be arbitrarily selected
and adjusted depending on the product and use, the coating may be
performed to a thickness of 1 .mu.m to 500 .mu.m, and, when the
thickness is outside the above range, the thermal conductivity may
be increased or the visible light transmittance may be reduced. The
coating layer may further have a UV and IR blocking function, and a
UV blocking layer and an IR blocking layer may be separately
laminated on the coating layer. The thermal insulation sheet using
the composition according to the present invention may have a
particle filling rate of 30% to 80%, a visible light transmittance
of 70% or more, and a thermal conductivity of less than 0.1 w/mk,
and thus, may have transparent thermal insulation properties.
[0100] Hereinafter, the present invention will be explained in more
detail by way of exemplary embodiments. These embodiments are
intended to only illustrate the present invention, and it will be
obvious to those skilled in the art that the scope of the present
invention is not construed as being limited to these embodiments.
Further, simple changes and modifications of the present invention
are appreciated as included in the scope of the invention.
[0101] Various physical properties of hollow silica particles and
thermal insulation sheets of examples and comparative examples were
measured by the above-described methods.
EXAMPLE 1
[0102] Water (150 ml) and phenyltrimethoxysilane (PTMS) (1 ml) were
put in a 250 ml flask and nitric acid (60%, 0.2 ml, 2.6 mmol) was
then added thereto and stirred at 60.degree. C. for 4 minutes.
Subsequently, ammonia water (30%, 10 ml, 308 mmol) was added to a
reaction solution and stirred at 60.degree. C. for 1 hour and 30
minutes to form a shell, and the inside of the shell was etched
with ethanol. The reactant thus obtained was filtered and dried at
120.degree. C. to obtain hollow silica particles.
[0103] As illustrated in the transmission electron microscope (TEM)
images of FIG. 2, the particles obtained were monodisperse
spherical particles and hollow particles in which a hollow, which
was seen to be bright, was formed. Refractive index, thermal
conductivity, oil absorption rate, porosity when mixed with a
resin, and particle distribution coefficient of variation (CV
value) of the particles are presented in Table 1.
EXAMPLE 2
[0104] Hollow silica particles were obtained in the same manner as
in Example 1 except that phenyltrimethoxysilane (PTMS) (0.8 ml) and
TEOS (0.2 ml) were mixed and used as the silane in Example 1, and
physical properties of the particles obtained are presented in
Table 1.
EXAMPLE 3
[0105] In Example 3, after the acidic solution was added in Example
1, the stirring times were respectively set as 9 minutes to
manufacture particles. The manufactured particles formed
monodisperse spherical hollow particles as illustrated in FIG. 4,
and physical properties are presented in Table 1.
EXAMPLE 4
[0106] In Example 4, sonication was further performed in Example 1
to manufacture particles. The manufactured particles formed
monodisperse spherical hollow particles as illustrated in FIG. 5,
and had a smooth surface almost without impurities and a true
sphere shape in comparison to the particles of Example 3. Physical
properties are presented in Table 1.
COMPARATIVE EXAMPLES 1 AND 2
[0107] In Comparative Examples 1 and 2, reactions were performed in
the same manner as in Example 1 except that the reactions were
respectively performed at 30.degree. C. and 85.degree. C. instead
of the reaction temperature in Example 1.
[0108] In Comparative Example 1, particles were not formed, and, in
Comparative Example 2, particles were formed, but a hollow was not
present as in FIG. 3.
COMPARATIVE EXAMPLE 3
[0109] In Comparative Example 3, after the addition of the acidic
solution as described in Example 1, stirring was performed for 15
minutes, and the results of the reaction are presented in Table 1.
Final particles were gelated and hollow particles were not formed.
This seemed to be due to the fact that small particles were
agglomerated because the stirring time was excessively
increased.
COMPARATIVE EXAMPLE 4
[0110] In Comparative Example 4, hollow silica particles were
obtained in the same manner as in Example 1 except that the
concentration of the silane in Example 1 was changed to 0.5 mol %.
As a result, hollow particles were formed, but a diameter of the
particles was greater than 1 .mu.m and physical properties suitable
for the manufacture of a thermal insulation sheet were not
obtained.
TABLE-US-00001 TABLE 1 Hollow Thermal Average Oil particle
Refractive conductivity particle absorption formation index (W/m K)
CV (%) diameter rate (ml/g) Porosity (%) Example 1 Formed 1.36 0.03
3 100 nm 0.018 90 Example 2 Formed 1.34 0.03 3.8 180 nm 0.015 95
Example 3 Formed 1.29 0.03 4 100 nm 0.018 92 Example 4 Formed 1.37
0.03 3 200 nm 0.021 93 Comparative Not formed -- -- -- -- -- --
Example 1 Comparative Not formed 1.45 0.043 4 100 nm -- -- Example
2 Comparative Not formed -- -- -- -- -- -- Example 3 Comparative
Formed 1.36 0.047 -- 2.4 .mu.m 0.019 -- Example 4
EXAMPLE 5
[0111] A composition was prepared by mixing 60 wt % of the hollow
silica particles manufactured according to Example 1 based on the
total composition, 30 wt % of polyimide (PI) resin, and organic
solvent and initiator as a remainder. One side of a PET film was
coated with the prepared composition by bar coating and was cured
for 20 seconds by using a UV lamp to manufacture a thermal
insulation sheet on which a 125 thick coating layer was formed.
Measurement results of physical properties of the thermal
insulation sheet are presented in Table 2.
EXAMPLES 6 AND 7
[0112] In Examples 6 and 7, compositions were prepared by
respectively mixing the hollow silica particles in ratios of 30 wt
% and 80 wt % based on the total composition in Example 5 and
thermal insulation sheets were then manufactured. Measurement
results of physical properties are presented in Table 2.
COMPARATIVE EXAMPLES 5 AND 6
[0113] Compositions were prepared by respectively mixing the hollow
silica particles in ratios of 20 wt % and 90 wt % based on the
total composition in Example 5, and, since coating was difficult
due to high viscosity of the liquid when the amount of the hollow
particles was 50% or more, methyl ethyl ketone (MEK) as an organic
solvent was used to adjust the viscosity to be low. Then, thermal
insulation sheets were manufactured and measurement results of
physical properties are presented in Table 2.
COMPARATIVE EXAMPLE 7
[0114] A thermal insulation sheet was manufactured in the same
manner as in Example 5 except that hollow particles having a
diameter of 200 nm and an inner diameter of a hollow portion of 100
nm, which were manufactured by a conventional template synthesis
method, were used, and measurement results of physical properties
of the thermal insulation sheet are presented in Table 2. In the
thermal insulation sheet, since the particles were not dispersed in
the composition and escaped from the resin during coating and UV
curing, a coating layer may not be formed.
[0115] In Examples 5 to 7 and Comparative Examples 5 to 7, since
the viscosity of the liquid was excessively high when the mixing
ratio of the hollow particles was greater than 50%, an organic
solvent having a low boiling point (BP) was added to reduce the
viscosity. Then, coating was performed, a solvent was evaporated by
primary drying, and UV curing was performed.
TABLE-US-00002 TABLE 2 Particle Dilution solvent mixing MEK (% with
Visible light Thermal ratio respect to hollow transmittance
conductivity (%) particles) (%) (W/m K) Example 5 60 10 90 0.05
Example 6 30 -- 92 0.08 Example 7 80 30 87 0.03 Comparative 90 40
60 0.03 Example 5 Comparative 20 -- 80 0.23 Example 6 Comparative
60 10 -- -- Example 7
[0116] As illustrated in Table 2, it may be understood that, since
the visible light transmittance was high when the mixing ratio of
the hollow particles was less than 30 wt % based on the total
composition, the thermal insulation sheet was transparent but the
thermal insulation efficiency was decreased due to the low air
content. In contrast, it may be understood that, since the visible
light transmittance was reduced when the mixing ratio of the hollow
particles was greater than 80 wt %, the thermal insulation sheet
was opaque and the curing efficiency was reduced due to a decrease
in the amount of the curing resin.
[0117] Also, in the particles manufactured according to Comparative
Example 7, large-sized pores were present on surfaces of the
particles. The resin was infiltrated into the hollow through the
pores on the surfaces during mixing with the UV curable resin, and
since the particles were not dispersed in the composition and
escaped from the resin during the coating and UV curing, a coating
layer may not be formed. Thus, it is considered that it is
difficult to manufacture a transparent thermal insulation sheet
having the properties of the present invention by using
conventional hollow silica particles.
* * * * *